The invention relates to improvements in density measuring apparatus and methods in general, and more particularly to improvements in apparatus for and in methods of measuring or ascertaining the density of successive increments of running flows (such as streams, rods, fillers or the like) of particulate fibrous material. Still more particularly, the invention relates to improvements in methods of and in apparatus for ascertaining the density of flows of accumulations of fibrous material of the type being manipulated in various types of machines which are utilized in the tobacco processing industry. Typical examples of such machines are those for the making of continuous rods which are ready to be subdivided into plain cigarettes, cigars, cigarillos or cheroots of unit length or multiple unit length.
It is already known to construct and assemble a cigarette rod making machine (also known as maker) in such a way that it can turn out a plurality of (particularly two) continuous cigarette rods wherein a rod-shaped filler of natural, artificial and/or reconstituted tobacco is draped into a continuous wrapper of cigarette paper or the like and is subdivided into plain cigarettes of unit length or multiple unit length. As a rule, successive increments of each filler of particulate fibrous material are being monitored in order to ascertain their density, i.e., a characteristic which is important to maintain the quality of the cigarettes within an acceptable range. Uniform density or a density which is maintained within a predetermined range is important to ensure that the quantity of tobacco from cigarette to cigarette, as well as within a discrete cigarette, does not fluctuate at all or fluctuates only within an acceptable range. Such uniform or practically uniform density can be achieved by ensuring that each of a short or long series of successively produced cigarettes (or cigars, cigarillos or cheroots) contains a predetermined quantity of particles as well as that the particles are uniformly distributed from end to end. The so-called filling power of rod-shaped smokers' products can be ascertained by determining, with a requisite degree of accuracy, the density of the rod-shaped fillers of such products.
As a rule, the density of fillers in cigarettes or analogous rod-shaped products of the tobacco processing industry (hereinafter referred to as cigarettes for short) is determined by resorting to a source of radioactive radiation, such as a strontium 90 preparation which emits beta rays. Reference may be had, for example, to U.S. Pat. No. 4,424,443. The drop in the intensity of radiation which has penetrated through a flow of tobacco particles is indicative of the density of successive increments of such flow. An advantage of a density measuring apparatus which employs a source of beta rays is that the results (namely the density measurements) are highly reliable. However, such apparatus also exhibit certain serous drawbacks, particularly as concerns their cost, because their installation in or their utilization in conjunction with cigarette rod making machines renders it necessary to carry out extensive, costly, complex and bulk-increasing undertakings to ensure the safety of attendants in a cigarette making plant.
It is also known to ascertain the density of a continuous flow of tobacco or analogous particulate material for use in the tobacco processing industry by employing a density measuring apparatus which is equipped with a source of infrared radiation. Reference may be had, for example, to U.S. Pat. No. 4,805,641. An advantage of such apparatus is that the aforediscussed undertakings to ensure the safety of attendants can be simplified or omitted. However, the reliability of an apparatus which operates with infrared radiation is not as satisfactory as that of an apparatus which operates with beta rays.
In accordance with a further proposal (disclosed in U.S. Pat. No. 3,056,026), the apparatus for monitoring the density of a flow of tobacco particles or other particulate material of the tobacco processing industry can employ a source of X-rays. However, presently known apparatus of such character have also failed to satisfy all of the requirements concerning the safety of the attendants, low cost, compactness, versatility and accuracy of determination of the density of successive increments of a rapidly running flow in the form of a rod, filler or stream of particulate material.
Another drawback of all heretofore known density measuring apparatus of the above outlined character is that they are incapable of simultaneously monitoring the densities of several rapidly advancing flows of particulate material which includes or consists of natural, artificial and/or reconstituted tobacco. On the other hand, many presently known cigarette makers are designed to simultaneously produce several continuous cigarette rods which can be subdivided into discrete files of plain cigarettes of unit length or multiple unit length. Reference may be had, merely by way of example, to U.S. Pat. Nos. 4,889,138, 5,009,238 and 5,072,741. Therefore, a machine which is designed to simultaneously turn out several continuous cigarette rods must be equipped or combined with a discrete density measuring apparatus for the particulate material of each cigarette rod. This contributes to the bulk and cost of such machines and renders it likely that the quality of density measuring operation which is carried by one density measuring apparatus will depart from the quality of the density measuring operation carried out by the other apparatus.
The disclosures of all patents which are enumerated in the specification of the present application are incorporated herein by reference.